Electrocatalytic oxidation of water at a polyoxometalate nanoparticle modified gold electrode

Electron-Sponge Nature of Polyoxometalates for Next-Generation Electrocatalytic Water Splitting and Nonvolatile Neuromorphic Devices

Designing next-generation molecular devices typically necessitates plentiful oxygen-bearing sites to facilitate multiple-electron transfers. However, the theoretical limits of existing materials for energy conversion and information storage devices make it inevitable to hunt for new competitors. Polyoxometalates (POMs), a unique class of metal-oxide clusters, have been investigated exponentially due to their structural diversity and tunable redox properties. POMs behave as electron-sponges owing to their intrinsic ability of reversible uptake-release of multiple electrons. In this review, numerous POM-frameworks together with desired features of a contender material and inherited properties of POMs are systematically discussed to demonstrate how and why the electron-sponge-like nature of POMs is beneficial to design next-generation water oxidation/reduction electrocatalysts, and neuromorphic nonvolatile resistance-switching random-access memory devices. The aim is to converge the attention of scientists who are working separately on electrocatalysts and memory devices, on a point that, although the application types are different, they all hunt for a material that could exhibit electron-sponge-like feature to realize boosted performances and thus, encouraging the scientists of two completely different fields to explore POMs as imperious contenders to design next-generation nanodevices. Finally, challenges and promising prospects in this research field are also highlighted.

New Water Oxidation Electrocatalyst Based on the Cobalt-Containing Polyoxometalate-Reduced Graphene Oxide Hybrid Nanomaterial

A new hybrid nanomaterial based on the immobilization of cobalt-containing polyoxometalate (CoPOM) on the surface of reduced graphene oxide (rGO) was designed for an efficient electrocatalytic water splitting reaction. First, the surface of rGO was functionalized with aminopropylsilyl groups and protonated with hydrochloric acid to produce ammonium groups. Then, the electrostatic interaction of positively charged rGO-supported ammonium groups with anionic CoPOM produced a CoPOM-APTS-rGO hybrid nanomaterial. The achieved hybrid nanomaterial exhibited a low overpotential of 128 mV versus NHE at a current density of 10 mA cm^-2 in the electrocatalytic water oxidation at pH 7. In addition, a fast reaction kinetic with a Tafel slope of 74 mV dec^-1 was seen in the presence of the prepared hybrid nanomaterial. Linear sweep voltammetry analysis revealed the long-term stability and activity of CoPOM-APTS-rGO for water oxidation in neutral conditions.

Simultaneous determination of methadone and morphine at a modified electrode with 3D β-MnO2 nanoflowers: application for pharmaceutical sample analysis

The present research synthesized manganese dioxide nano-flowers (β-MnO₂-NF) via a simplified technique for electro-catalytic utilization. Moreover, morphological characteristics and X-ray analyses showed Mn in the oxide form with β-type crystallographic structure. In addition, the research proposed a new efficient electro-chemical sensor to detect methadone at the modified glassy carbon electrode (β-MnO₂-NF/GCE). It has been found that oxidizing methadone is irreversible and shows a diffusion controlled procedure at the β-MnO₂-NF/GCE. Moreover, β-MnO₂-NF/GCE was considerably enhanced in the anodic peak current of methadone related to the separation of morphine and methadone overlapping voltammetric responses with probable difference of 510 mV. In addition, a linear increase has been observed between the catalytic peak currents gained by the differential pulse voltammetry (DPV) of morphine and methadone and their concentrations in the range between 0.1–200.0 μM and 0.1–250.0 μM, respectively. Furthermore, the limits of detection (LOD) for methadone and morphine were found to be 5.6 nM and 8.3 nM, respectively. It has been found that our electrode could have a successful application for detecting methadone and morphine in the drug dose form, urine, and saliva samples. Thus, this condition demonstrated that β-MnO₂-NF/GCE displays good analytical performances for the detection of methadone.

Electrochemical sensor based on β-MnO₂ nanoflower-modified glassy carbon electrode for the simultaneous detection of methadone and morphine was fabricated.